Candida albicans, the most frequently isolated human fungal pathogen, has developed several mechanisms to evade immune detection and killing. First, Candida is able to mask immunogens in its cell wall. Second, upon phagocytosis by macrophages, Candida is able to undergo hyphal morphogenesis. These filamentous cells are able to pierce through the macrophage and release the fungus to infect other tissues. New technologies, including high-throughput FACS, genome-wide lentivirus RNAi libraries, and gene deletion libraries now allow for the systematic identification of host (macrophage) and pathogen (Candida) pathways that are fundamental to fungal pathogenesis. The identification of such pathways is essential for the development of new pharmaceutical targets that either specifically target Candida or stimulate enhanced macrophage/immune function. The goals of my proposal are to: 1. Use genome-wide RNAi libraries to identify macrophage genes required for phagocytosis of C. albicans and the induction of filamentation of phagocytosed Candida. 2. Identify Candida albicans mutants that have increased exposure of signature cell surface components by high throughput FACS and determine their role in responses inflammatory and phagocytic responses by macrophages. 3. Utilize the Candida cell surface mutants together with the macrophage knockdown lines to reconstruct the pathogen-macrophage recognition pathway. Relevance to public health: Systemic Candida infection is a life-threatening condition that has a mortality rate of 40%. The studies I have proposed will identify both fungal and host processes required for the success of Candida as a pathogen. Understanding the methods that Candida uses to avoid detection and killing by the immune system is the first step towards development of drugs to block these processes.